The disclosure relates to coating apparatus and methods. More particularly, the disclosure relates to application of thermal barrier coatings for gas turbine engines.
Gas turbine engine gaspath components are exposed to extreme heat and thermal gradients during various phases of engine operation. Thermal-mechanical stresses and resulting fatigue contribute to component failure. Significant efforts are made to cool such components and provide thermal barrier coatings to improve durability.
Exemplary thermal barrier coating systems include two-layer thermal barrier coating systems. An exemplary system includes a NiCoCrAlY bond coat (e.g., low pressure plasma sprayed (LPPS)) and a yttria-stabilized zirconia (YSZ) thermal barrier coat (TBC) (e.g., air plasma sprayed (APS)). While the TBC layer is being deposited or during an initial heating cycle, a thermally grown oxide (TGO) layer (e.g., alumina) forms atop the bond coat layer. As time-at-temperature and the number of cycles increase, this TGO interface layer grows in thickness. U.S. Pat. Nos. 4,405,659 and 6,060,177 disclose exemplary systems.
Exemplary TBCs are applied to thicknesses of 5-40 mils (127-1016 micrometer) and can provide in excess of 300° F. temperature reduction to the base metal. This temperature reduction translates into improved part durability, higher turbine operating temperatures, and improved turbine efficiency.
Examples of coating apparatus are found in U.S. Pat. No. 8,709,160, of Neal et al., Apr. 29, 2014, and U.S. Pat. No. 9,133,542, of Neal et al., Sep. 15, 2015, which disclose use of thermal hoods to maintain part temperature. U.S. Pat. No. 8,951,350, of Neal et al., Feb. 10, 2015 discloses a removable hood liner. Thermal hoods are typically either in the form of an arcuate plate or plate assembly (e.g., a sector of a circular cylindrical shell) or a flat top plate or plate assembly.
It is also known to have an adjustable height top plate or hood instead of a fixed hood.